In general, a hydraulic construction machine, such as a hydraulic excavator, includes a diesel engine as a prime mover. At least one variable displacement hydraulic pump is rotated by the engine, and a plurality of hydraulic actuators are driven by a hydraulic fluid delivered from the hydraulic pump, thus performing necessary work. The diesel engine is provided with input means for commanding a target revolution speed, e.g., a throttle dial, to control a fuel injection amount in accordance with the target revolution speed, whereby the revolution speed is controlled. Also, the hydraulic pump is provided with absorption torque control means for horsepower control to control a pump tilting to be reduced such that pump absorption torque will not exceed a preset value (maximum absorption torque) when the pump delivery pressure rises.
Regarding that type of hydraulic construction machine, a technique for the so-called auto-acceleration control is disclosed in Japanese Patent No. 3419661, for example. The term “auto-acceleration control” means a technique of lowering the target revolution speed of the engine to save energy when an operation input from a control lever is small, and of raising the target revolution speed of the engine to ensure workability when the lever operation input is increased.                Patent Document 1: Japanese Patent No. 3419661        